1. Field of the Invention
The present invention relates to a method of forming a pattern of a first material on a surface of a second material, and in particular to a method of punch or press forming a pattern of the first material in a surface of a carrier material, and of then punch or press transferring the pattern from the surface of the carrier material to the surface of the second material.
2. Description of the Prior Art
In manufacturing magnetic memory circuit cards, wafers of vicalloy are formed at preselected locations on a surface of a substrate, which is generally comprised of aluminum, and wires are then extended across the wafers to permit electrical pulses to "read" information stored on the wafers. Vicalloy is a generic term (p. 405, Ferromagnetism by Bozarth, 1st ed., pub. 1951 by Van Norsten), used to designate those materials typically comprised of 52% cobalt, 37.25% iron, 10% vanadium, 0.050% manganese and 0.026% silicon, and is laminated on an aluminum substrate for manufacturing magnetic memory cards.
In one common manufacturing process a resist pattern, which outlines the wafers, or magnets, is applied by heretofore known techniques on the exposed vicalloy surface. During ensuing processing, approximately 92% of the vicalloy is dissolved in an aqueous etchant solution comprised of ammonium persulfate (a powerful oxidizing agent) highly acidified with sulfuric acid, for leaving a magnet wafer pattern on the substrate. Except that the etched silicon will precipitate from the etchant in the form of silicon dioxide, the spent etchant will contain dissolved salts of all of the other foregoing metals of vicalloy.
Such a process for forming a pattern of vicalloy wafers on a substrate has certain disadvantages. One disadvantage, for example, is that the process of forming the magnet pattern, i.e., laminating, resist patterning and etching, is time consuming and expensive. Another is that the ammonium persulfate spent as etchant has an impurity concentration exceeding that which will permit disposal thereof in a sewer, and must therefore be depurated prior to disposal, also an expensive and time consuming procedure, not to mention that 92% of the vicalloy, a reasonably expensive material, is wasted.
A technique which overcomes the disadvantages of fabricating magnetic memory cards by etching vicalloy is set forth in U.S. Pat. No. 3,847,700, which issued on Nov. 12, 1974, based upon an application filed Nov. 17, 1972, and which is assigned to the assignee of the present invention. In that application, a magnetic memory circuit card is fabricated by positioning a thin sheet of vicalloy material over a surface of either an aluminum or an epoxy glass substrate, and by striking the sheet of vicalloy with a multiprojectioned punch to embed wafers of the vicalloy material into the surface of the substrate in a desired pattern. If the substrate is made of aluminum, warping of the substrate may occur when the wafers are embedded therein, which requires that the substrate be flattened, or straightened, for use in a magnetic memory circuit card. If the substrate is of an epoxy glass material, warping of the substrate does not occur when vicalloy wafers are embedded therein, or if a slight degree of warping does occur the substrate, with the wafers embedded therein, may readily be straightened by being pressed between a pair of flat, heated plates. The use of an aluminum substrate is preferred, however, in the fabrication of a magnetic memory circuit card, in that the switching characteristics exhibited by a wafer embedded in the aluminum substrate are enhanced by the generation of eddy-currents in the aluminum substrate when a wafer embedded therein is pulsed with a current through a wire extended thereacross.
Another technique for forming a pattern of a metal on a surface of a substrate is disclosed in U.S. Pat. No. 2,969,300, which issued on Jan. 24, 1961, to E. E. Franz. This technique contemplates positioning a thin sheet of the metal over an adhesive coated surface of a resilient tape, and striking the metal sheet with a punch to remove a pattern of metal from the sheet and to position the pattern in the adhesive on the tape. The tape is then positioned adhesive side down, and therefore metallic pattern side down, over an adhesive coated surface of the substrate. The tape and the substrate are then pressed together and heated to cure the adhesive, and the tape is then peeled away from the substrate to leave behind the metallic pattern, embedded in the adhesive on the surface of the substrate, on the substrate.
A disadvantage of this technique is that the metallic pattern on the surface of the substrate is contaminated on the upper surface thereof with the adhesive that was on the tape when the pattern was initially adhesively secured thereto, which could render the pattern bearing substrate unsuitable for certain electronic uses. Also, if this technique were employed in the fabrication of magnetic memory circuit cards, such that a sheet of vicalloy positioned over an adhesive coated surface of a paper tape is struck with a multiprojectioned punch to embed wafers of the vicalloy material into the adhesive on the tape in a desired pattern, the wafers could "swim" in the adhesive on the tape and lose their positioning with respect to each other, and thereby move out of a desired pattern. Thereafter, when the wafers are transferred to an adhesive coated surface of a substrate, they would not be on the surface of the substrate in the desired pattern, which would render the substrate unsuitable for use as a component in a magnetic memory circuit card since each wafer on the substrate must be in a precise position with respect to every other wafer so that it will underlie a selected one or more of a plurality of wires which are extended across the surface of the substrate in a predetermined position with respect to the wafers.